Beam expanders are a type of optical device that expands the size of a collimated beam of light. In some cases, beam expanders are used as intracavity or extracavity components for lasers. Some beam expanders are telescopic in nature. These telescopic beam expanders can be refractive or reflective telescopes. In tunable laser resonator applications, intracavity beam expansion can illuminate the entire width of a diffraction grating and reduce beam divergence. This effect can enable the emission of very narrow linewidths, for example, for use in analytical applications such as laser spectroscopy. In laser propagation applications, extracavity beam expansion can be used to minimize the divergence of the laser illumination. This effect maximizes the laser energy over longer path lengths which, for example, improves the performance of remote sensing applications such as direct detection and coherent laser radars.
Current beam expanders are rather large and difficult to manufacture, The size of current system makes them unsuited for some applications where space is at a premium. Other refractive beam expanders, with a 5x magnification have an overall length from 275 mm to as long as 375 mm. Some applications require optical systems that do not obscure any portion of the laser beam. Some reflective systems, obscure the laser beam. In other eases, the application, such as scanning systems, requires an external entrance or exit pupil. Some beam expanders, specifically Galilean telescope designs, do not provide an external pupil location. Current systems also have difficulty operating consistently in harsh temperature conditions. There are some applications that require diffraction limited performance over temperature ranges from −40 degrees Celsius to +75 degrees Celsius. Existing beam expanders are not designed for these harsh temperatures.